As is well known in the art that hydromechanical control systems including compensator valves are used to control the operation of hydraulic motors by sensing pressure differences across the control ports of the hydraulic motor. Such a conventional hydromechanical control system is shown in FIG. 1.
The compensator valve of the conventional hydromechanical control system shown in FIG. 1 is designed to sense the pressure difference across the motor control ports of the hydraulic motor.
The conventional hydromechanical control system shown in FIG. 1 particularly provides a direct acting compensator valve 10 which performs the control function based upon the difference in pressure between low pressure fluid flowing from a low pressure control flowing to the high pressure control port 13 of the motor.
The high pressure fluid flowing to the high pressure control port 13 of the motor is supplied to high pressure input 14 of the valve 10 and the low pressure fluid from the low pressure control port 11 of the motor is supplied to low pressure input 15 of the valve 10.
The compensator valve 10 shown in FIG. 1 detects the difference between the high pressure input 14 and the low pressure input 15 and provides a control signal through control ports 11 and 13 which actuates the hydraulic motor control piston at some predetermined design pressure thereby controlling the apparatus being controlled. Particularly, the control signal feeds hydraulic fluid to the control piston of the hydraulic motor 12 which then varies the displacement of the hydraulic motor 11.
To complete the hydraulic loop a fluid return 16 is also provided in the system for returning excess fluid to a fluid reservoir.
The compensator valve 10 shown in FIG. 1 provides a housing having an elongated bore 17 formed therein. A plurality of openings are formed in the housing corresponding to the high and low pressure input ports 14 and 15. The high pressure input port 14 inputs high pressure fluid at a first end of the bore 17. The high pressure control port 13 is also at the first end of the bore 17. The low pressure input port 15 inputs low pressure fluid from the low pressure control port 11 of the motor into a low pressure chamber which communicates with a second end of the elongated bore 17.
A spool 18, movably positioned in an axial direction in sealed slidable engagement in the elongated bore 17, forms a high pressure first chamber at the first end of the elongated bore 17.
A portion of the spool 18 is disposed near the opening to the high pressure control port 13 such that the spool 18 when moved controls the flow of fluid through the opening to the high pressure control port 13. The movement of the spool 18 occurs in response to a difference in pressure between the high and low pressure fluids supplied by the high and low pressure inputs 14 and 15.
A large spring 20 is provided in the low pressure chamber. The large spring 20 biases the spool 18 against forces generated by the high pressure fluid in the high pressure chamber at the first end of the elongated bore 17.
The compensator valve 10 operates by detecting predetermined differences in pressure between the high pressure fluid and the low pressure fluid. A detected difference between the high pressure fluid and low pressure fluid of a predetermined amount causes movement of the spool 18 in the axial direction thereby varying the opening of the high pressure control port 13. By varying the opening of the high pressure control port 13 the pressure and flow of the control signal output thereby is varied.
The large spring 20 is used to supplement the force generated by the low pressure fluid in the low pressure chamber by biasing the spool 18 against the force generated by the high pressure fluid in the high pressure chamber. Such biasing of the spool 18 against the force generated by the high pressure fluid aids in detecting the difference in pressure of a predetermined amount between the high pressure fluid and the low pressure fluid. Further, due to the much greater force generated by the high pressure fluid relative to the low pressure fluid, it is necessary that the large spring 20 be of sufficient size to adequately supplement the force generated by the low pressure fluid so that a balance is established in the valve for reasonably responsive functioning.
The conventional compensator valve shown in FIG. 1 works well when used in 1,000-5,000 psi hydraulic systems. Moderately sized large springs can be designed to withstand such pressures and balance the forces generated by the high and low pressure fluids.
However, the conventional compensator valve shown in FIG. 1 suffers from the disadvantage of not working well in high pressure hydraulic systems that operate between 5,000-8,000 psi. The size of the spring needed to balance pressures between 5,000-8,000 psi would be extremely large. A valve using an extremely large spring for balancing is unacceptable in designs where space is at a premium. Further, the valve, due to its size, may not be as responsive as desired.
Various other conventional compensator valves have been proposed. Such conventional compensator valves are disclosed in U.S. Pat. Nos. 3,017,897; 3,706,322; 4,187,884 and 4,649,957.
The conventional compensator valves disclosed by the above-referenced patents suffer from the disadvantage of not adequately addressing the problems associated with providing a compensator valve for a high pressure hydromechanical control system that is relatively small in size.